1. Field of the Invention
The present invention relates to an alkaline battery separator, i.e., a separator for an alkaline battery, and a process for producing the same.
2. Description of the Related Art
An alkaline battery separator composed of a hydro-entangled nonwoven fabric containing fine fibers derived from dividable composite fibers has many fine voids formed between the fine fibers, and accordingly has an excellent electrolyte-holding capacity.
For example, Japanese Unexamined Patent Publication (Kokai) No. 7-147154 discloses an alkaline battery separator prepared by imparting a hydrophilic property to a hydro-entangled nonwoven fabric composed of polyolefin fibers, which are mainly fine fibers, derived from polyolefin dividable composite fibers, and an alkaline battery separator prepared by adhering the hydro-entangled nonwoven fabric with polyolefin heat-sensitive-adhesive fibers having a lower melting point. The alkaline battery separators composed of mainly fine fibers derived from the dividable composite fibers have an excellent electrolyte-holding capacity. Further, the alkaline battery separator adhered with the polyolefin heat-sensitive-adhesive fibers has an excellent tensile strength.
Nevertheless, the breaking strength of the alkaline battery separators disclosed in Japanese Unexamined Patent Publication (Kokai) No. 7-147154 is insufficient. For example, when the alkaline battery separators are rolled together with electrode plates upon assembling an alkaline battery, the separators are easily broken by the edges of the electrode plates. The separators also have the disadvantages of a low yield and an inconsistent battery performance.
Further, Japanese Unexamined Patent Publication (Kokai) No. 7-29561 discloses an alkaline battery separator composed of wet-laid hydro-entangled nonwoven fabric prepared by hydro-entangling (1) 60 to 80% by weight of dividable composite fibers (fiber length=5-15 mm) consisting of polyolefin polymer and ethylene vinyl alcohol polymer, (2) 20 to 30% by weight of heat-sensitive-adhesive fibers, and (3) 10-20% by weight of synthetic fibers (fiber length=5-15 mm) having a denier larger than those of fine fibers derived from the dividable composite fibers and the heat-sensitive-adhesive fibers. The alkaline battery separator has an excellent electrolyte-holding capacity and tensile strength, but the hydrophilic nature of the alkaline battery separator is imparted only by the dividable composite fibers. Therefore, it is necessary to raise the ratio of the dividable composite fibers, and thus, the ratio of the synthetic fibers having a denier larger than those of the fine fibers and heat-sensitive-adhesive fibers is lower. As a result, some alkaline battery separators have an insufficient breaking strength.